This invention is in the field of vapor-phase methods of growing semiconductor layers, and is particularly concerned with those methods using organometallic vapors. In a specific case of the method whereby mercury cadmium telluride alloys are grown, gaseous cadmium and tellerium alkyls pyrolytically decompose in the vicinity of a heated substrate contained in a mercury vapor atmosphere. The cadmium, tellerium and mercury combine on the substrate to form the alloy. Heretofore, the substrate and means for providing the mercury vapor have been heated by two different heaters, since two different temperatures are required. Unfortunately, these two heaters, with their controls and connections, make the system for carrying out the method unnessarily cluttered and complicated. The method whereby these disadvantages is overcome is shown in my copending U.S. patent application Ser. No. 426,428, filed Sept. 29, 1982, now U.S. Pat. No. 4,439,267, issued Mar. 27, 1984. The susceptor as used in that copending invention is shown in this application.